Ice, Snow, and Glaciers and the Water Cycle

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Ice and glaciers are part of the water cycle, even though the water in them moves very slowly. Ice caps influence the weather, too. The color white reflects sunlight (heat) more than darker colors, and as ice is so white, sunlight is reflected back out to the sky, which helps to create weather patterns. Read on to learn how glaciers and ice caps are part of the water cycle.

Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human interference.

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Water stored as ice is part of the water cycle

Satellite image of the North Pole area showing massive amounts of water stored as ice.

The Arctic region holds a massive amount of ice. Perhaps what is most striking in this picture is the extent of the Greenland icecap — almost the whole island is overlain by a huge and deep (almost three miles deep in places) sheet of ice. The Greenland icecap averages almost a mile in thickness and contains about 10 percent of the total ice mass on the globe. (Credit: NASA)

The water cycle describes how water moves above, on, and through the Earth. But, in fact, much more water is "in storage" at any one time than is actually moving through the cycle. By storage, we mean water that is locked up in its present state for a relatively long period of time. Short-term storage might be days or weeks for water in a lake, but it could be thousands of years for deep groundwater storage or even longer for water at the bottom of an ice cap, such as in Greenland. In the grand scheme of things, this water is still part of the water cycle.

 

Ice caps around the world

Map of where glaciers and ice caps exist on Earth.
Credit: National Geographic

The white areas in this map show glaciers and ice sheets around the world (reproduced from National Geographic WORLD, February 1977, no. 18, p. 6, with permission). The vast majority, almost 90 percent, of Earth's ice mass is in Antarctica, while the Greenland ice cap contains 10 percent of the total global ice mass. The Greenland ice cap is an interesting part of the water cycle. The ice cap became so large over time (about 600,000 cubic miles (mi3) or 2.5 million cubic kilometers (km3)) because more snow fell than melted. Over the millennia, as the snow got deeper, it compressed and became ice. The ice cap averages about 5,000 feet (1,500 meters) in thickness, but can be as thick as 14,000 feet (4,300 meters). The ice is so heavy that the land below it has been pressed down into the shape of a bowl. In many places, glaciers on Greenland reach to the sea, and one estimate is that as much as 125 mi3 (517 km3) of ice "calves" into the ocean each year—one of Greenland's contributions to the global water cycle. Ocean-bound icebergs travel with the currents, melting along the way. Some icebergs have been seen, in much smaller form, as far south as the island of Bermuda.

 

Ice and glaciers come and go, daily and over millennia

The climate, on a global scale, is always changing, although usually not at a rate fast enough for people to notice. There have been many warm periods, such as when the dinosaurs lived (about 100 million years ago) and many cold periods, such as the last ice age of about 18,000 years ago. During the last ice age much of the northern hemisphere was covered in ice and glaciers, and, as this map from the University of Arizona shows, they covered nearly all of Canada, much of northern Asia and Europe, and extended well into the United States.

Glaciers are still around today; tens of thousands of them are in Alaska. Climatic factors still affect them today and during the current warmer climate, they can retreat in size at a rate easily measured on a yearly scale.

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Here is a satellite image of Iceland in the late summer, showing ice-free landscape except for permanent ice fields. Even in summer the large permanent ice caps stand out brightly against the volcanic rock surrounding them. The brightly colored lakes and coastal waters are the result of very fine and highly reflective sediment that is ground into bits by the immense weight of glaciers and washed out to sea with glacial runoff (at the bottom of picture).

Next seen is an image of Iceland in the middle of winter, showing that the island country is almost completely covered in white snow and ice, obscuring the permanent glaciers and icecaps that exist year-round. Over millennia, ice has carved out deep fjords leaving fringes of land that extend like fingers into the ocean, as seen in the northwestern coast.

Glacier worldwide are shrinking in size

Grinnell Glacier, with dates showing the retreat of the glacier from 1850 to 2005

Grinnell Glacier, Montana (Credit: Lisa McKeon, USGS)

This picture shows the Grinnell Glacier in Glacier National Park, Montana, USA in 2005. The glacier has been retreating rapidly since the early 1900's. The year markers point to the former extent of the glacier in 1850, 1937, 1968, and 1981. Mountain glaciers are excellent monitors of climate change; the worldwide shrinkage of mountain glaciers is thought to be caused by a combination of a temperature increase since the Little Ice Age, which ended in the latter half of the 19th century, and increased greenhouse-gas emissions.

 

Ice caps influence the weather

Just because water in an ice cap or glacier is not moving does not mean that it does not have a direct effect on other aspects of the water cycle and the weather. Ice is very white, and since white reflects sunlight (and thus, heat), large ice fields can determine weather patterns. Air temperatures can be higher a mile above ice caps than at the surface, and wind patterns, which affect weather systems, can be dramatic around ice-covered landscapes.

 

Some glacier and ice cap facts

Bering Glacier in Alaska is the largest glacier in North America. This NASA satellite view shows how a glacier is similar to a river.
(Credit: NASA Earth Observatory)
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  • Glacial ice covers 10-11 percent of all land.
  • According to the National Snow and Ice Data Center (NSIDC), if all glaciers melted today the seas would rise about 230 feet (70 meters).
  • During the last ice age (when glaciers covered more land area than today) the sea level was about 400 feet (122 meters) lower than it is today. At that time, glaciers covered almost one-third of the land.
  • During the last warm spell, 125,000 years ago, the seas were about 18 feet (5.5 meters) higher than they are today. About three million years ago the seas could have been up to 165 feet (50.3 meters) higher.
  • Largest surface area of any glacier in the contiguous United States: Emmons Glacier, Washington (4.3 square miles or 11 square kilometers)

 

Ice caps and global water distribution

Even though the amount of water locked up in glaciers and ice caps is a small percentage of all water on (and in) the Earth, it represents a large percentage of the world's total freshwater. As these charts and the data table show, the amount of water locked up in ice and snow is only about 1.7 percent of all water on Earth, but the majority of total freshwater on Earth, about 68.7 percent, is held in ice caps and glaciers.

Bar chart showing the distribution of water on, in, and above the Earth.

One estimate of global water distribution

Water source Water volume, in cubic miles Water volume, in cubic kilometers Percent of total water Percent of total freshwater
Ice caps, Glaciers, & Permanent snow 5,773,000 24,064,000 1.7% 68.7%
Total global freshwater 8,404,000 35,030,000 2.5% --
Total global water 332,500,000 1,386,000,000 -- --

Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp. 817-823.

 

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